failing vs weakness

failing and weakness both are nouns.

Word	Noun	Adjective	Verb	Adverb
failing	Yes	Yes	No	No
weakness	Yes	No	No	No

As nouns, failing and weakness are synonyms defined as:

failing (noun)	weakness (noun)
failure to reach a minimum required performance	the property of lacking physical or mental strength; liability to failure under pressure or stress or strain
a flaw or weak point	powerlessness revealed by an inability to act
	a penchant for something even though it might not be good for you
	a flaw or weak point
	the condition of being financially weak

failing (adjective)	weakness (adjective)
below acceptable in performance